Geology and Mhieralogy. 151 



observes that the Mesozoic strata of the Great Basin are thickest 

 to the westward, being 5,000 feet on its southwestern border ; in 

 the High Plateaus of Southern Utah, 3,000 feet ; and in New 

 Mexico, if the Zuni sandstone be excluded, barely 2,000 feet. 

 The Cretaceous is somewhat thinner in New Mexico than in 

 Utah, and much thinner to the eastward in Texas. The facts 

 are supposed to indicate a western origin for the great Mesozoic 

 sediments. 



Captain Dutton connects the upward flexing of the strata in the 

 Zuni plateau with the upward protrusion of a boss of underlying 

 Archaean. He observes that in the " mountain platforms of Colo- 

 rado the rising bosses of granite have not only flexed up the beds 

 on the sides of the ranges, but have caught remnants of them 

 within their disturbed tracts and carried them up with them, 

 bending, warping and twisting them, shattering and faulting 

 them." 



In this Rocky mountain type of mountain structure, which in- 

 cludes as one of its varieties the vast monoclinal uplifts, the 

 lifting force, Captain Button observes, acted vertically from 

 beneath ; and any appearances of a horizontal force are such as 

 have resulted from the vertical movements. Archaean rocks 

 hence are often the center or core of the mass. The fault-planes 

 in the case of some of the monoclinal uplifts are believed to be 

 vertical or nearly so, and therefore to accord with the theory of 

 uplift by action from beneath.' 



Captain Dutton recognizes thus that the pitch of the fault- 

 planes, in the case of the grander faults of a mountain region, 

 bears strongly on the question as to the method of mountain- 

 making concerned ; prevailing low angles being as good evidence 

 of lateral thrust as very high angles are of subvertical thrust ; 

 and no more important subject remains for investigation in the 

 west than that relating to the dip of the planes in the grand 

 monoclinal faults, about which little is yet positively known. 

 The Appalachians of eastern Amei'ica and the Juras and Alps in 

 Europe are admitted to be wholly of different structure and 

 mode of origin, lateral thrust having been somehow concerned in 

 their formation. Captain Dutton's last sentence expresses in a 

 word his own opinion, and that of most investigators in the 

 region: "The mountains of the West have not been produced 

 by horizontal compression, but by the action of some unknown 

 forces- which have pushed them up." j. d. d. 



. 3. ^Etudes sur les Bilobites et autres fossiles des Quartzites de 

 la base du Systeme Silurique da Portugal, par J. F. N. Delgado, 

 Chef de la Section des Travaux Geologiques, Mem. de l'Acad. R. 

 Sci. Lisbonne. 114 pp., 4to, with 42 plates. Lisbonne, 188Q< — 

 This memoir on the Bilobites, or the so-called fossil Algae of the 

 Lower Silurian, and especially those of the lowest quartzyte of 

 the Silurian (Cambrian) of Portugal, by the distinguished head 

 of the geological survey of Portugal, is a most forcible reply to 

 the arguments and evidence presented by Mr. Nathorst of Sweden 



